typedef struct elf32_rel {
  Elf32_Addr	r_offset;//got
  Elf32_Word	r_info;//idx
} Elf32_Rel;

typedef struct elf32_rela{
  Elf32_Addr	r_offset;//got
  Elf32_Word	r_info;//idx
  Elf32_Sword	r_addend;
} Elf32_Rela;

typedef struct elf32_sym{
  Elf32_Word	st_name;//offset
  Elf32_Addr	st_value;
  Elf32_Word	st_size;
  unsigned char	st_info;
  unsigned char	st_other;
  Elf32_Half	st_shndx;
} Elf32_Sym;

typedef struct elf64_rel {
  Elf64_Addr r_offset;	/* Location at which to apply the action */
  Elf64_Xword r_info;	/* index and type of relocation */
} Elf64_Rel;

typedef struct elf64_rela {
  Elf64_Addr r_offset;	/* Location at which to apply the action */
  Elf64_Xword r_info;	/* index and type of relocation */
  Elf64_Sxword r_addend;	/* Constant addend used to compute value */
} Elf64_Rela;

typedef struct elf64_sym {
  Elf64_Word st_name;		/* Symbol name, index in string tbl */
  unsigned char	st_info;	/* Type and binding attributes */
  unsigned char	st_other;	/* No defined meaning, 0 */
  Elf64_Half st_shndx;		/* Associated section index */
  Elf64_Addr st_value;		/* Value of the symbol */
  Elf64_Xword st_size;		/* Associated symbol size */
} Elf64_Sym;

_dl_fixup (
# ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
           ELF_MACHINE_RUNTIME_FIXUP_ARGS,
# endif
           struct link_map *l, ElfW(Word) reloc_arg)
{
  const ElfW(Sym) *const symtab
    = (const void *) D_PTR (l, l_info[DT_SYMTAB]);
    //获得STMTAB地址

  const char *strtab = (const void *) D_PTR (l, l_info[DT_STRTAB]);
    //获得STRTAB地址

  const PLTREL *const reloc
    = (const void *) (D_PTR (l, l_info[DT_JMPREL]) + reloc_offset);
    //获得Elf_rel地址

  const ElfW(Sym) *sym = &symtab[ELFW(R_SYM) (reloc->r_info)];
    //获得ELF_sym地址
  const ElfW(Sym) *refsym = sym;
  void *const rel_addr = (void *)(l->l_addr + reloc->r_offset);
    //获得GOT结构体地址
  lookup_t result;
  DL_FIXUP_VALUE_TYPE value;
  assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT);
    //某些检查
  if (__builtin_expect (ELFW(ST_VISIBILITY) (sym->st_other), 0) == 0)
    {
      const struct r_found_version *version = NULL;
      if (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
        {
          const ElfW(Half) *vernum =
            (const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]);
          ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)] & 0x7fff;
          version = &l->l_versions[ndx];
          if (version->hash == 0)
            version = NULL;
        }
      /* We need to keep the scope around so do some locking.  This is
         not necessary for objects which cannot be unloaded or when
         we are not using any threads (yet).  */
      int flags = DL_LOOKUP_ADD_DEPENDENCY;
      if (!RTLD_SINGLE_THREAD_P)
        {
          THREAD_GSCOPE_SET_FLAG ();
          flags |= DL_LOOKUP_GSCOPE_LOCK;
        }
#ifdef RTLD_ENABLE_FOREIGN_CALL
      RTLD_ENABLE_FOREIGN_CALL;
#endif
    //下面部分通过在libc中search "string" 获得real_address
      result = _dl_lookup_symbol_x (strtab + sym->st_name, l, &sym, l->l_scope,
                                    version, ELF_RTYPE_CLASS_PLT, flags, NULL);
      /* We are done with the global scope.  */
      if (!RTLD_SINGLE_THREAD_P)
        THREAD_GSCOPE_RESET_FLAG ();
#ifdef RTLD_FINALIZE_FOREIGN_CALL
      RTLD_FINALIZE_FOREIGN_CALL;
#endif
      /* Currently result contains the base load address (or link map)
         of the object that defines sym.  Now add in the symbol
         offset.  */
      value = DL_FIXUP_MAKE_VALUE (result,
                                   SYMBOL_ADDRESS (result, sym, false));
    }
  else
    {
      /* We already found the symbol.  The module (and therefore its load
         address) is also known.  */
      value = DL_FIXUP_MAKE_VALUE (l, SYMBOL_ADDRESS (l, sym, true));
      result = l;
    }
  /* And now perhaps the relocation addend.  */
  value = elf_machine_plt_value (l, reloc, value);
  if (sym != NULL
      && __builtin_expect (ELFW(ST_TYPE) (sym->st_info) == STT_GNU_IFUNC, 0))
    value = elf_ifunc_invoke (DL_FIXUP_VALUE_ADDR (value));
  /* Finally, fix up the plt itself.  */
  if (__glibc_unlikely (GLRO(dl_bind_not)))
    return value;
  return elf_machine_fixup_plt (l, result, refsym, sym, reloc, rel_addr, value);
}